The mucosal epithelium is a primary barrier against invasive microbes, so understanding the physicochemical forces involved in mucosal immune surveillance may be critical to understanding pathogenesis versus immunity. Mucosal M cells overlying lymphoid tissues are central to immune surveillance, using mechanisms for active uptake of mucosal pathogens. Ironically, many invasive pathogens ranging from Salmonella to Anthrax are also adept at using M cells for entry across the epithelial barrier. How is this uptake mediated? Recently, we showed that low ionic strength in the liquid of the airway lumen significantly enhanced particle uptake by M cells. Low ionic strength should increase long-range electrostatic interactions and increase the repulsion of negatively charged particles from negatively charged epithelium; curiously, we found a paradoxically increased uptake at M cell apical membranes in vivo. This finding has given rise to our working hypothesis: in contrast to neighboring mucosal epithelial cells, the M cell is electrostatically optimized for interaction wit microparticles in suspension as an emergent property of its smooth apical membrane. The differences in surface charge establishes an electrostatic field at the boundary between enterocytes and M cells that helps draw negatively charged particles to the M cell apical membrane. We propose two aims to test this hypothesis: (1) We will use cell culture models and a modified tangential flow chamber to model the binding of particles at the apical surface of the epithelial cells with different surface charge characteristics. We will compare fluorescent microbes and PLGA microparticles produced with different surface zeta potentials to assess binding to enterocyte versus M cell-like smooth apical membranes. (2) Using mouse models of M cell deficiency, we will study the effect of particle surface charge on uptake in the intestine, and the effect of electrostatic forces on M cell- dependent versus -independent particle uptake to immune tissues. An understanding of the effect of these electrostatic forces in the intestine will be important in defining the mechanisms of M cell mucosal immune surveillance. In addition, these forces would be expected to be important in the pathogenesis of invasive microbes such as Salmonella. Finally, our studies will help define requirements for designing mucosal vaccine delivery systems, whether designed for M cell targeted uptake or for nonspecific adhesion and M cell-independent uptake.